Automatic manipulator apparatus have been developed for work operations such as welding, assembly, removal and handling of parts, and other types of repetitive work cycles. Some of these manipulators are programmable and allow the manipulator to be reused for different tasks requiring different sequences of movements through a variable work space.
One type of programmable multi-axis automatic assembly system is shown in U.S. Pat. No. 4,275,986 to Engelberger et al., which discloses a manipulator having six axes of motion for great flexibility in sequencing of movement and positioning of the manipulator hand. This type of manipulator, as well as many other similar articulated-arm devices, is for some applications too large, expensive, and complex. For many basic pick-and-place operations, use of hydraulic power or precision encoder position control is simply overengineering.
At the opposite extreme of parts manipulation devices are apparatus such as disclosed in U.S. Pat. No. 3,947,208 to Broderick. This device finds application in press molding machines and the like, and includes an extracting arm mounted on a translating and rotating drive shaft moved by the opening of the mold. A cam mechanism causes the arm to swing into the space between mold halves and grip the parts, and to thereafter swing out of the machine and release the part. Although the device is comparatively simple and inexpensive, it is a dedicated device, not reprogrammable, and suffers especially from the drawback that it is unable to extract a part, reorient the part to another plane, and discharge the part at a remote workstation. Such operations are frequently desirable for removing parts from a molding machine and placing the parts on a conveyor belt for further processing.
For injection molding factories, plant layout requirements sometimes dictate that molding machines be placed relatively close to one another, thereby limiting the amount of space available for a parts manipulator to remove the molded parts. There is often insufficient space for installation of a conventional multi-axis robotic manipulator. Even though smaller and lighter electrically driven manipulators having articulated joints are now commonly available, space limitations sometimes preclude use of these articulated-joint mechanisms because entry of the manipulator hand into the mold and retraction of the part forces the articulated arm to assume awkward positions as the hand is guided between the tie bars of the molding machine and into the mold cavity between the mold halves. In some applications, it may be impossible to apply an articulated-arm manipulator whose elbow might interfere with other machinery as the manipulator assumes its various positions in extracting and removing the parts.
In applications where space is at a premium, telescoping boom devices such as shown in U.S. Pat. No. 3,916,701 to Butler have been proposed. This patent discloses an industrial robot for grasping, manipulating and moving parts including a telescoping boom assembly mounted for movement about two orthogonal axes and a part gripper mounted on the forwardmost end of the telescoping boom assembly. The part gripper is rotatably movable about a third axis which is substantially parallel to the longitudinal axis of the telescoping boom assembly. The gripper in this patent is rotated about its axis by a rotary actuator mounted within the forwardmost telescoping boom element and includes an hydraulically actuated linear-to-rotary converter.
One problem with the Butler and other prior art parts manipulators is that they are frequently large and heavy machines designed for industrial environments requiring handling of articles through precise programmed movements. For removal of molded parts from an injection molding machine, there is seldom need for precision movement in engaging an article in the molding machine and removing the article to a remote work station such as a conveyor belt. There is also seldom need for high powered hydraulic actuator mechanisms since injection molded pieces typically are small and lightweight when compared to comparably sized metal articles. Yet, flexibility in sequence and extent of movement is a desireable feature.
Accordingly, there is the need for a simple, inexpensive, lightweight, and small parts manipulator having movement and sequence flexibility and suitable for use in parts extraction from molding machines. Such a manipulator must successfully enter the space between the mold halves, engage or grasp the molded parts, retract the molded parts, and place the parts at a remote work station such as on a conveyor belt or the like.